1. Field of the Invention
The invention relates to a temperature sensor, particularly a PTC temperature sensor of the generic type and a method for producing a temperature sensor.
2. Background Information
It is generally known for temperature sensors having temperature sensor elements made of temperature-resistant resistance materials having a temperature-dependent resistance value to be used (cf. E. D. Macklen, "Thermistors" Verlag Electrochemical Publications [Electrochemical Publications Press], Ltd., 1979) for measuring relatively high temperatures such as those which prevail in the exhaust gases of internal-combustion engines.
PTC temperature sensors use the continuous resistance change of metals or semiconductors having a positive temperature coefficient when temperatures change. The metals which are preferably used in PTC temperature sensors are platinum and nickel, as well as their alloys, because of their high stability and reproducibility.
It is furthermore known, for example from EP-A 0,188,900 and 0,142,993, and DE-OS 3,017,947 and 3,543,759, for planar exhaust gas sensors to be used in order to determine the lambda value of gas mixtures, which exhaust-gas sensors can be produced in a particularly cost-effective manner using ceramic-film and screen-printing technology.
It is known from DE-PS 3,733,192 for the aging resistance and the response times of PTC temperature sensors to be improved by hermetically encapsulating the PTC temperature sensor elements with respect to the gas being measured and the environmental air.
It is a disadvantage of the known PTC temperature sensor elements that they have a certain area extent and are thus not subjected to the same exhaust-gas temperature at all points.